1. Field of the Invention
A tone transposing apparatus whereby each sound produced is systematically different in pitch from that normally associated with the digital struck.
2. Description of the Prior Art
With an organ tuned in the conventional equitempered scale, a musical composition may have all of its tones uniformly raised or lowered by a pitch changing mechanism; it will be recognized in that case as being the same composition, pitched higher or lower. Such a pitch changing mechanism is useful when a singer is accompanied by an organ or piano, for the singer often wishes the absolute pitch of the accompaniment to be changed higher or lower than the music is written. While transposition by an octave up or down is comparatively easy, such octave transpositions are usually of too large a magnitude. Experience has shown that an accompanist who can play by ear in four well separated keys can accommodate most musical compositions to a particular group of voices.
In order to accompany other musical instruments, it is desirable to be able to set a pitch changing apparatus to a standard position in which middle A has a fundamental frequency of 440 Hz. Since other musical instruments may be playing in different keys, the pitch changer should preferably be able to shift to other absolute pitches for the musical output which differ from standard absolute pitch by a integral number of semitones.
Transposition of written music can be accomplished, without changing the fingering of the music as written, by means of a pitch changing switch which alters the couplings between the tone generators and the digitals which actuate them. Such a switch changes all tones uniformly by a selected amount--for example, three semitones upward.
Bode, in U.S. Pat. No. 3,023,659, and Derry, in U.S. Pat. No. 3,674,907 have disclosed pitch changing apparatus in which the pitch of only the top octave of tone generators is switched; lower octaves of tones are derived from the top octave by twelve chains of frequency dividers. The Bode apparatus has a standard state and eleven transported states, allowing selection from a total of twelve different absolute pitches for the musical output. The apparatus has twenty-three audio input leads and twelve audio output leads.
Most musical instruments do not presently contain pitch changers, mainly because of their size and expense.